What are they capable of?

[digitS']

My good south window in the house has just been changed and the finish on the sill has dried so the plants were moved back in and the greenhouse furnace turned off last night. I am able to fit 12 containers with seedlings on that window sill and a table, inches away. With only 7 containers so far (5 more on top the fridge and more to be started any day), I've got a few more days that the seedlings can stay indoors before I run out of room. That will save me a little $$.

Okay, the weather has been real nice lately. It was 30 outdoors at 7:30am with a lovely blue sky. With no furnace on, it was 36 inside the greenhouse.

Last night, I closed things down about 4pm when I brought the seedlings in. Outdoors, the temperature was over 50 and the temperature in the greenhouse was nearly 80. Fifteen hours later, the temperature had fallen - a lot.

My 9' by 20' greenhouse is really a "sunshed" -- it has a cedar sided, framed and insulated north wall and roof. The angle of the south wall is really best for January sun rather than March sun but it's doing fine right now. The interior of the north wall is foil-covered insulation board. My thought was to maximize light thru the winter rather than retain heat. There is a concrete foundation but the floor is dirt.

Commercial greenhouses are often kept at 60F overnight and that is where I set my thermostat when I have the furnace running. Certainly, plants may not die at lower temperatures but too cold and too great a fluctuation between day and night temperatures can interfere greatly with growth.

There you have it: The greenhouse is only 6 above outdoor temperatures after just over, 12 hours of night-time darkness.

Steve

 

[ducks4you]

WOW!! It takes these kinds of times for us to really be serious about our costs. Keep us up to date!!

 

[digitS']

I set up my 9' by 20' hoop house the day before yesterday. It doesn't much matter what the temperature gets down to at night - there's nothing much I can do about it anyway. Unlike the greenhouse, the hoop house has no heater. Daytime temps . . . I gotta watch it like a hawk.

Ventilation is me opening the window or me opening the door. Even so, on a sunny day with the high temperature reaching nearly 60F and with very limited air movement, it can rise to 80 with both door and window open wide!

Anyway, this morning at 7:30am it was 33 outdoors. In the hoop house (1 layer, 6 mil plastic) the temperature was 36. There isn't anything in there that would be harmed by even a light frost so it isn't of much concern. Asian brassicas and lettuce seed have been sown. Soon, there will be some bok choy transplanted to the remaining open ground of the 2 raised beds.

I wanted to mention something about the "thermal mass" idea. Modern commercial greenhouses are built with aluminum - there's a lot of reflective qualities to aluminum.

When I worked in a commercial greenhouse - aluminum construction was just hitting it's stride. However, most of the greenhouses that covered the acre where I worked, were wood. A couple, had been built during the 1920's. (There were actually greenhouses at that location prior to that time but nothing remained of them. )

Anyway, every board, metal support, everything in those greenhouses that could be painted, was painted white. White, white, white - the better to reflect sunlight back to what was actually "green." That is, the plants.

So you see, there is the value of heat retention but there is also the value of maximizing light, usually during the time of the year when light is limited. In fact, in a greenhouse used for flower production - 3 of the most important flower holidays (Thanksgiving, Christmas, & Valentines Day) are in low-light months.

Doubling up on glazing will limit light reaching the plants. It may retain heat but with less sunlight, there's less heat to retain within the structure. And, if you paint the back wall black to absorb the light, that's light that could have been reflected onto your plants. Compromises! Life is full of compromises .

Steve

 

[vfem]

You have much patience to go through all this. It does seem you have some happy plants going now. And you are so sure they are going to adapt well.

I'll be planning the greenhouse game soon enough, probably just not this year. The little cold frame (4'x4' cube of windows) does really well even when it was in the 20's at night. I used no more then some black none slip tool box liners on the bottom and a milk jug full of water wrapped in black plastic. It kept the temps at night over freezer the best I could tell. In the mornings when I checked it was never until 35.

 

[lesa]

vfem, have you tried covering your little greenhouse with a blanket on those cool nights? I think it makes a big difference here, even with frost....What about covering things inside a big greenhouse or hoop house? We are still down in the teens at night, so I am not using my cold frames yet- hoping for April 1!

 

[digitS']

vfem, have you tried covering your little greenhouse with a blanket on those cool nights? I think it makes a big difference here, even with frost....What about covering things inside a big greenhouse or hoop house? We are still down in the teens at night, so I am not using my cold frames yet- hoping for April 1!

And, there is the best way to conserve heat, Lesa!

It might be a fairly simple thing to run a curtain inside my greenhouse to use at night. Since I have never used it outside of the spring months, it was never fitted with one. The fact that it is only open on the south side and half of the east and west sides would make it easier to retrofit with a curtain.

A hoop house could have "little hoopies" inside. How much that would help, I'm not sure.

The greenhouse fuel bill would be terrible during many of the very cold weeks of winter, as it is. The things just cannot hold heat well without the sun. Whatever the glazing - there is almost no insulation value. Once that sun is shining, however, the BTU's climb ! In a large greenhouse, it is really quite remarkable to see the roof vents open during a sunny afternoon when the temperature is below freezing outdoors .

I used to try to think how an insulated garage door might be useful for overnight insulation. If the glass wall is vertical, some sunlight is reflected. Still, it may matter very little - think of a large, vertical wall of glass and a tiered plant stand inside . . . then think of going outside in the evening and closing a garage door in front of that wall .

A good deal of rigid foam insulation could make a good deal of difference for a heating bill.

Steve

 

[vfem]

Oh I forgot to mention, our evenings are generally in the upper 40's and some lower 50's now. I don't see one evening in the next couple weeks where it would get under 45. Everything here is going to do peachy.

I have opened the cold frame door everyday, and even starting hardening off most of my sprouts outside almost 2 weeks ago. I also transplanted and moved out some basil and a gerber daisy. (Which I was THRILLED to discover yesterday, that my gerber daisies from last year over wintered, and are coming back!!!!!)

 

[digitS']

Yesterday was just a terrible weather day:

Freezing at dawn
Windy all day, with gusts above 30mph
Snow, sleet, and/or rain every hour

The TeeVee lady had promised us some sun breaks -- It Did Not Happen! There was some easing of the cloud cover.

The greenhouse doesn't matter -- the furnace has been on in there for 3 weeks. It was just that light wasn't any good for growing.

The tunnel started off the day at 39F. The highest temperature outdoors was 40 but the tunnel, with only a single sheet of 6mil plastic, stayed at least 6 or 8 above that thru the day.

During a brief period of "more light" - the temperature in the tunnel actually rose quite a bit above 70. Then the storms moved in again.

Perhaps some wonder why I'm recounting all of this. I suppose it is to encourage people to have furnaces put into their greenhouses if they want to make good use of them a couple months before last frost. But, also important, is using the simplest of protected growing space, a plastic tunnel, to grow cool-season starts either in the ground or in containers.

Nothing but the hardiest of weed seeds have germinated outdoors. During the warm spell we had about a week ago, I measured the soil temperature. At 2" depth, it was 41. Nothing in the way of a vegetable seed has germinated yet, outdoors.

Within that tunnel, I've got a seedling multitude of lettuce, bok choy, and other greens! It has been as cold as 27 overnight but hasn't frosted inside the tunnel yet. Not much warmer but . . . warmer.

I'm going to have all sorts of plants to move out of both structures into the garden! Some things, will stay right where they are growing. Easily, easily, easily - it will be a 3 week jump on the season. More likely, it will be a 5 week jump or even greater.

I've used greenhouses since the mid 1970's. They have limits, don't think otherwise. Still, they have uses .

Steve

 

[digitS']

Here are the growing beds within the tunnel, a little later in the season on an earlier year:

Here are some plants that I had thinned a little earlier. They are on their way out into the open garden:

Right now, everything is very tiny but they are on their way . . .

:tools

 

[obsessed]

niCE! VERY NICE! Way to extend your season.